The invention relates to a device for CD reproduction with variable speed or direction. The field of application of the invention relates to CD playback devices, in particular devices that are compatible with a CD player, such as, for example, DVD players which are likewise suitable for the playback of CDs or corresponding CD-ROM drives, which enable data or information stored on a CD to be reproduced with an increased or reduced speed and also with a variable direction. Aspects of the invention are, inter alia, an improved comprehensibility of the reproduced information, fast and accurate moving to desired positions, and also reverse playback.
During a fast forward run or reverse run, known audio CD players have only a low comprehensibility of the reproduced information. Between short sequences which are played back at normal speed, a wide jump to the next sequence is carried out, so that the feeling of a fast forward run is imparted to the user.
During the jumping from one sequence to a next sequence, which, as a rule, is carried out over a plurality of tracks, no information is read from the recording medium, with the result that data are read into a buffer memory in a discontinuous sequence and gaps arise between the reproduction sequences. Although the information reproduction takes place at normal speed or in real time, the user can hardly follow the playback progress on account of a low comprehensibility or a low deducibility of the reproduced information. It proves to be very difficult to follow the information reproduced in fragments and to deduce the content thereof and also to stop or begin the reproduction at a desired position.
The object of the invention, therefore, is to provide CD playback devices which enable CD reproduction with variable speed or direction in conjunction with improved deducibility or comprehensibility of the reproduced information, with a low outlay.
According to the invention, this object is achieved by means of the features specified in main claims. Advantageous designs and developments are specified in subclaims.
The invention is based on the fact that the data or information read from the CD are read into a buffer memory at a rate which, as a rule, is higher than is required for real-time reproduction. This is applicable for example to vibration-resistant CD playback devices, CD-ROM drives and also to DVD playback devices.
Vibration-resistance CD playback devices have a buffer memory into which data or information read from the recording medium are read at a doubled rate, as a rule, and are read out at a normal rate for reproduction. An electronic control unit ensures that by targeted jumping-back of the pick-up, the continuity of the data stream is ensured and the buffer memory is filled to a maximum extent. The size of the buffer memory is then the decisive factor regarding the length of time that the playback device is capable of interruption-free reproduction of information or data of the recording medium when there is an interruption of the data stream read from the recording medium. Furthermore, vibration-resistant CD playback devices are known in which the rate at which data are read from the CD is regulated as a function of the occupancy of the buffer memory.
In a CD-ROM drive, which, as a rule, is connected to a computer, the hard disk or a virtual memory can be used as a buffer memory of appropriate capacity. DVD playback devices are also intended to be able to play compact discs or normal audio CDs. For this purpose, the same hardware as is necessary for the playback of DVDs is then used. That is to say that a large buffer memory is available into which the data from the CD are read at a higher rate than in the case of normal CD players. In this case, too, an electronic control unit ensures that by targeted jumping-back of the scanning unit or the pick-up, the continuity of the data stream in the buffer memory is preserved. This surplus of data read from the CD is advantageously used, according to one aspect of the invention, for CD reproduction with variable speed in conjunction with improved comprehensibility of the reproduced information.
In contrast to the solution known from the prior art, individual sequences of the recording medium are not reproduced discontinuously, rather the data of the recording medium are read from the buffer memory without any gaps, or continuously, with subsampling for the purpose of a fast forward run or with oversampling for the purpose of slowing down the reproduction speed.
An information reading means with which the reproduction speed is set is provided for this purpose in the device for CD reproduction with variable speed. The information reading means comprises a read-write controller for the buffer memory, which controller, according to the respective design, is optionally connected to a FIFO and a D/A converter. The units that are already present in CD playback devices or in CD-compatible devices can thus advantageously be used, according to a second aspect of the invention, for the fast forward run, slowing down the reproduction speed or also reverse playback with improved comprehensibility of the reproduced information. In the fast forward run, the data are read from the buffer memory at an increased rate compared with normal operation, by skipping samples. The data are read into the buffer memory likewise at a rate which is higher than a rate required for real-time reproduction or for reproduction during normal operation. This advantageously reduces the number of returns compared with normal operation. The reproduction with improved comprehensibility is achieved by the fact that using an electronic control unit, data read from the CD are read in an ordered sequence to a buffer memory as a continuous digital data stream, or read from the buffer memory with sub- or oversampling and are reproduced as a continuous data stream. In the case of subsampling, only every second or nth sample is read from the buffer memory by the information reading means and joined together to form a continuous data stream. The result of the subsampling is then a data stream having a doubled or n-fold rate. The subsampling also leads to the known frequency increase, where it has emerged, however, that an improved comprehensibility is achieved in comparison with the known reproduction of segments at normal speed with gaps. Furthermore, it has been found that a higher repetition rate of skipped samples leads to less aliasing than a lower repetition rate. Sharing out information omissions over an information period has a less disturbing effect than a concentrated appearance of the same information loss. On account of the improved comprehensibility of the reproduced information, the playback progress of the CD can be better followed and, as a result, according to a further aspect of the invention, it is possible to move to a desired position or passage with higher accuracy. The read-write controller present in CD or CD-compatible devices can be induced to effect the sub- or oversampling for the purpose of changing the CD reproduction speed by means of an input signal. In the case of oversampling, which leads to the CD reproduction speed being slowed down, samples stored in the buffer memory are read out a number of times in accordance with the slowing-down rate and joined together to form a continuous data stream. It is thereby possible to move to a desired position or passage with high precision.
A further aspect of the invention consists in changing the reproduction direction or reverse playback of a CD. In principle, the reproduction of information stored on a CD in the reverse direction by reversing the scanning direction is not possible on account of the type of modulation that is used and a bit sequence that must be observed. The filling-in of bits that is connected with the type of modulation chosen for CDs, in 8-to-14 modulation, and the insertion of coupling bits require that information stored on the CD be played back or reproduced in the forward direction. Furthermore, reverse scanning would cause the order of MSB and LSB to be interchanged. Despite these obstacles, CD reproduction in the reverse direction is enabled in the following manner:
scanning direction or direction of rotation of the CD corresponding to the direction used in normal operation,
reading of a first predetermined number of subcode blocks into the buffer memory
reproduction or read-out from the buffer memory beginning at the last sample in the last subcode block of the first predetermined number of subcode blocks through to the first sample of the first subcode block,
requesting of a second predetermined number of subcode blocks from the recording medium which lie before the output block of subcode blocks.
This requesting or the reading into the buffer memory must already be concluded before the read-out of the first sample of the first subcode block of the first predetermined number of subcode blocks in order that the second predetermined number is available for read-out immediately after the output of the first predetermined number. A predetermined number of 50 subcode blocks, which corresponds to a reproduction time of approximately 0.66 second at normal speed, has proved to be advantageous in the case of an audio CD.
A further aspect of the invention is CD reproduction with a very high speed. For reproduction with a y-fold speed, ranges of a predetermined number of subcode blocks, which number is 50, for example, are then reproduced and (yxe2x88x921)xc2x7n subcode blocks are then skipped. The subcode blocks that are reproduced or read from the buffer memory are likewise joined together to form a continuous data stream. The continuous data stream is then reproduced at a normal rate. However, it is also possible firstly to buffer-store this data stream and then subject it once again to sub- or else oversampling. An improved comprehensibility is achieved by the multistage sampling and combination of sub- and oversampling, particularly at very high reproduction speeds.